Even more evidence diminishing arguments that sexual orientation is a choice has emerged courtesy of U.S. scientists. The findings, announced at the American Association for the Advancement of Science in Chicago on Thursday, come about after a study of 400 gay men. Upon testing the DNA of all participants, scientists found that genes on at least two chromosomes affected whether or not a man was gay.

A region of the X chromosome called Xq28 had some impact on men's sexual behaviour – though scientists have no idea which of the many genes in the region are involved, nor how many lie elsewhere in the genome.

Another stretch of DNA on chromosome 8 also played a role in male sexual orientation – though again the precise mechanism is unclear.

Researchers have speculated in the past that genes linked to homosexuality in men may have survived evolution because they happened to make women who carried them more fertile. This may be the case for genes in the Xq28 region, as the X chromosome is passed down to men exclusively from their mothers.

"The study shows that there are genes involved in male sexual orientation," said Northwestern University psychologist Michael Bailey, who announced the findings at the conference.

"Sexual orientation has nothing to do with choice," he continued. "We found evidence for two sets [of genes] that affect whether a man is gay or straight. But it is not completely determinative; there are certainly other environmental factors involved."

But before the American Family Association rushes out to research in utero gaydar tests, Bailey's colleague Alan Sanders advises caution.

"When people say there's a gay gene, it's an oversimplification," Sanders said. "There's more than one gene, and genetics is not the whole story. Whatever gene contributes to sexual orientation, you can think of it as much as contributing to heterosexuality as much as you can think of it contributing to homosexuality. It contributes to a variation in the trait."

I like men because men are gorgeous, and muscular male bodies are the impersonation of harmony, beauty and strength. It's so simple. I don't give a f*ck about genes, divine or biological laws, social standards, etc.